Generally, silica particles show high oil absorption and high level filling with said particles is difficult to attain. Accordingly, it is difficult to produce high-fill silica-polymer composite materials and the like. Even when high level filling with silica and the like is possible, the materials obtained have unsatisfactory physical properties, as discussed below, and can hardly be submitted to practical use.
Thus, for example, in the case of silica-polymer composite materials prepared by random closest filling with powdery or flaky quartz glass powder, the maximum fill is 77% by weight. In the case of high silica-filled composite materials having a three-dimensional structure as synthesized from compatible polymer blend systems in a phase separation system utilizing the sol-gel process, the maximum fill is 80% by weight.
Although composite materials prepared from resins or the like with an inorganic material such as silica or glass have an increased rigidity (elasticity) with an increase in fill percentage, they have a decreased impact resistance, among others, and are hard and fragile or brittle. As a result, the high silica or like material-filled composite materials mentioned above are thus poor in shock resistance and like properties. Epoxy resin-based composite materials high filled with an inorganic material such as silica or glass, for instance, rapidly lose their rigidity at temperatures above the glass transition point of the resin. They are thus poor in high temperature stability.